Electrically driven vehicles are gaining more and more importance for meeting different individual mobility requirements. In particular, the electric bicycle is on the rise. An electric bicycle is a bicycle having an electric motor as an auxiliary drive. An electric drive assistance is conventionally requested by way of pedaling pedals which are fastened to the pedal cranks of the bicycle when the pedals are alternately pressed downward in a correspondingly pronounced manner. A chain ring is mounted on the pedal cranks in order to transmit a torque to the drive wheel of the bicycle, the drive wheel typically being the rear wheel, and the chain ring being coupled via a chain to a pinion which is mounted on the rear wheel in a torsionally rigid manner in the drive direction. The electric motor is conventionally accommodated in the hub of the rear wheel as a hub motor, the supply of which with electric power is brought about by rechargeable battery cells. The strength of the pedaling is detected by way of a torque measuring device, the electric power being called up from the rechargeable battery cells by way of a control device in a manner which corresponds to said torque measuring device, which electric power is fed to the hub motor for the auxiliary drive of the electric bicycle.
For the torque measuring device, it is known to use a measuring sleeve which is installed on the hub of the rear wheel. The measuring sleeve is made from non-magnetic material which is provided with a corresponding magnetization pattern which changes under the action of a torque on the measuring sleeve. This change in the magnetization pattern can be detected with the aid of an electrically operated coil pair, as a result of which a conclusion can be made about the magnitude of the torque. In order to tap off the magnetization pattern, the coil pair is arranged immediately adjacent to the measuring sleeve. Moreover, for sufficiently accurate measurement of the torque, the measuring sleeve is provided with a correspondingly long measuring section and the measuring sleeve is mounted in a radially and axially stable manner at its two longitudinal ends.
This results in the problem that the cabling of the coil pair is difficult and the measuring sleeve disadvantageously requires a large amount of installation space at the hub.